Polyphenylene ether resins have long been recognized as useful thermoplastic materials for a wide range of applications. Such polyphenylene ether aromatic compositions have superior physical, electrical and thermal properties as well as excellent hydrolytic and dimensional stability.
Polyphenylene ether compositions are combinable with alkenyl aromatic compositions (such as polystyrene) in virtually all proportions and have been improved by the addition of various impact modifiers when additional impact strength is desired. Such impact modifiers are typically natural or synthetic rubber compounds including polymeric and copolymeric compounds such as butadiene rubber, EPDM rubber, di- and triblock copolymers of styrene and butadiene, as well as other elastomeric products. Many of these are commercially available from a variety of sources.
One of the most important impact modifiers for polyphenylene ether-alkenyl aromatic compositions is a saturated rubber known as Kraton G, available from Shell Chemical Company. Kraton G is a saturated triblock copolymer styrene-butadiene-styrene or styrene-ethylene-butylene-styrene (SEBS rubber). These compounds afford useful impact strength improvements as well as superior thermal aging performance. The latter property is especially important in polyphenylene ether-alkenyl aromatic compositions designed for medium to high heat requirement applications. Such superior performance, however, has been achieved at relatively great expense compared to conventionally available impact modification systems and many manufacturers have sought to improve the properties of polyphenylene ether-alkenyl aromatic compositions with other impact modifier candidates.
It has now been discovered that useful polyphenylene ether compounds can be provided which exhibit an improved combination of impact strength and thermal stability in many thermoplastic applications. This improvement is achieved by a combination of the base resin and a modifying compound comprising a crosslinked acrylate core surrounded and interpenetrated by a crosslinked styrene shell. This crosslinked core-shell modifier appears to improve the properties of the basic polyphenylene ether-alkenyl aromatic resin without suffering from the thermal degradation often experienced by conventional modifiers of the unsaturated, i.e. non-hydrogenated type.